In the field of impact printers, certain design goals have included the concepts of low cost production along with low power consumption and low cost operation. A number of the previous impact printers used electromagnetic solenoids for moving certain parts of the printer such as the print hammers, however these solenoids consumed energy in amounts considered larger than necessary or economically feasible if lower costs were to be maintained.
Since impact printers commonly have included a platen with characters thereon for impact by the print hammers, the platen also required some type of drive means for positioning the platen for printing the proper characters at the exact instant in time. In the case of the very successful drum-type printer, the drum served as a platen and required a drive member or mechanism to rotate the drum at the desired speed. Additionally, the paper or like record media needed to be advanced after the completion of a line of printing.
Printing mechanisms have also included type racks carrying a plurality of type characters thereon and adapted to be positioned in one of a plurality of positions when printing takes place upon actuation of a printing element against the type character.
Representative prior art in the type character rack concept is U.S. Pat. No. 1,863,098, issued to C. Borel on June 14, 1932, and disclosing apparatus for computing statistical data which includes a cam on the drive shaft which raises a bar to enable release of the type elements to be driven to printing position. Type hammers impact the type elements against the paper and against a platen, and electromagnets are energized to attract and release the armatures for permitting movement of the type elements.
U.S. Pat. No. 1,902,060, issued to P. Dechene on Mar. 21, 1933, discloses printing mechanism with certain members biased upwardly by springs against a locking pawl. A rack member meshes with a gear which is pivoted to a lever biased by a spring and another gear carries a disc with type indicia thereon. A magnet releases the locking pawl to permit travel of the rack members upward and latch the gear to position the type indicia relative to the platen.
U.S. Pat. No. 3,241,756, issued to G. Schenk on Mar. 22, 1966, discloses printing mechanism for calculating machines having pinions meshing with teeth of type bars which include type faces thereon. A slide member is shiftable along the type bars, and a plate portion thereof has a hub and a ramp engageable against a rod when the type bars are in a raised position. The type hammers are immediately rotated to cam the type bars against the platen.